QUENCHING OF SINGLET OXYGEN

On the involvement of singlet oxygen in mutation induction by 8-methoxypsoralen and UVA irradiation in Escherichia coli K-12

The possible mutagenic effects induced by single oxygen, which is formed during UVA irradiation of bacterial cells pretreated with 8-methoxypsoralen (8-MOP), were investigated. As genetic endpoint, black mutation from arg-56 to arg+ was assayed in strain Escherichia coli K-12/343/113/uvrB; this system, in preliminary experiments, was rather sensitive to 8-MOP-induced photodynamic effects. To assess the involvement of singlet oxygen (1O2) in the mutation induction process, 2 tests were applied, namely, comparative mutation induction in D2O and H2O media (pH 7.0) and quenching of 1O2 with 1,4-diazabicyclo[2.2.2]octane (DABCO). When photodynamy was performed with the indicator cells suspended in D2O buffer, the mutagenic effect was substantially higher than that obtained with cells suspended in H2O buffer; this increase was even more pronounced when the incubation mixtures were thoroughly oxygenated before irradiation. D2O itself was not mutagenic under th present experimental conditions. Addition of DABCO in concentrations of 0.1--10 mM to the irradiation mixtures effectively reduced the number of 8-MOP-induced mutant yields by about 40%. DABCO itself had no effect on cell viability or on spontaneous mutation frequency under our experimental conditions. From these 2 sets of results, and from the preliminary findings that the photomutagenic effect of 8-MOP is higher in the uvrB derivative than in the corresponding excision-repair-proficient parent strain, which is in concordance with previous observations in other E coli strains, it can be concluded that 1O2 generated upon UVA irradiation of 8-MOP solutions is probably responsible for part of the observed genetic effects.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--part III: free radical transfer from oxidizing lipids

Parallels and similarities in chemical and functional damage to proteins by ionizing and uv radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma-radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Kinetics of accumulation of a photodynamically induced cell-surface polypeptide in a species of Arthrobacter

Cells of a species of Arthrobacter were incubated in the light with methylene blue, a dye that sensitizes photooxidative reactions by the production of singlet oxygen. An early and major response by the cells to these conditions was stimulation of synthesis of a single cell-surface polypeptide, 21,000 daltons in mass. The rate of synthesis of this polypeptide reached a maximal level about 30 min after the start of illumination. As a consequence, the amount of this polypeptide increased at least 10-fold during a period of 5 h. The presence of histidine or methionine, scavengers of singlet oxygen, markedly diminished synthesis and accumulation of this polypeptide. Concomitant with the accumulation of this polypeptide on the cell surface was the appearance of an extensive array of pili.

A possible mechanism of the generation of singlet molecular oxygen in nadph-dependent microsomal lipid peroxidation

A simplified system, consisting of NADPH, Fe3+-ADP, EDTA, liposomes, NADPH-cytochrome c reductase and Tris - HCl buffer (pH 6.8), has been employed in studies of the generation of singlet oxygen in NADPH-dependent microsomal lipid peroxidation. The light emitted by the system involves 1deltag type molecular oxygen identifiable by its characteristic emission spectrum and its behavior with beta-carotene. The generation of another excited species (a compound in the triplet state) could be demonstrated in this system by changes of light intensity and emission spectra which arise from photosensitizer (9,10-dibromoanthracene sulfonate, eosin, Rose-Bengal)-mediated energy transfers. Chemiluminescence in the visible region was markedly quenched by various radical trappers and by an inhibitor of NADPH-cytochrome c reductase, but not by superoxide dismutase. During the early stage of lipid peroxidation, the intensity of chemiluminescence was proportional to the square of the concentration of lipid peroxide. These characteristics suggest that singlet oxygen and a compound in the triplet state (probably a carbonyl compound) are generated by a self-reaction of lipid peroxy radicals.